Many municipalities and industries, including agricultural facilities, treat solid and liquid waste streams in anaerobic treatment facilities. Anaerobic digestion relies upon anaerobic microorganisms, e.g., methanogens, to convert, for example, sewage sludge, industrial and municipal waste, and biomass material, to valuable biogases, principally methane. The process has advantages not only in its suitability for treating wastes having a high water content or difficulties in incineration, but also facilitates the recovery of methane as a source of clean energy and reduces the volume of residual solids requiring processing and disposal.
Large agricultural operations may utilize confinement barns to house a large number of livestock, such as swine, poultry or dairy cows, in a relatively small land area. These agricultural operations often experience potential pollution problems relating to the handling and treatment of manure and wastewater. For example, pollution problems associated with animal waste include nitrogen, phosphorus, solids, bacteria and foul odors that result from anaerobic storage of manures. Storage lagoons or basins are often created on sites of agricultural operations to accumulate and store the flushed wastewater, feces and urine until an appropriate time to distribute the wastes over the land. Typically, during the storage process, due to the large volume of animal waste entering the lagoon, there is insufficient oxygen present to support the growth of aerobic cultures and/or aerobic biological activity. The absence of the necessary oxygen and the highly concentrated manure constituents convert microbial growth in the lagoon to anaerobic activity. This anaerobic activity leads to what is commonly known as a “septic” lagoon. In a septic lagoon, a very foul odor is present from the production of hydrogen sulfide, organic-sulfide compounds, organic acids, etc. Environmental concerns in wastewater treatment of agricultural operations thus focus generally on odor and water quality issues.
One method of wastewater treatment involves the addition of iron to anaerobic digesters to control hydrogen sulfide, phosphate, and scaling, and to provide micronutrients. The added iron, however, is not regenerated to substantially economize its use. Aggressive oxidation of waste by, for example, extreme pressure, high temperature, and/or acidification, solubilizes particulates and chemically digests organic material but the conditions required of such processes are prohibitively expensive. Mild oxidation of raw wastewaters is inefficient for regenerating iron within waste sludges and present risks to anaerobic digesters. Treatment of waste with pressure, while effective at solubilizing particulate matter, does not result in the regeneration of iron.
Cost-effective and practical methods and apparatuses for wastewater treatment that maximize iron utility in a wastewater treatment system, enhance anaerobic digestion of wastewater solids, and improve yield of fuel and energy values are thus desirable.